1. Technical Field
The present invention relates to a coordinate measuring auxiliary tool, a coordinate measuring probe and a coordinate measuring machine, more particularly, to a coordinate measuring auxiliary tool, which is suitable for a ball probe of a manual operation type three-dimensional coordinate measuring machine or digitizer and capable of easily and accurately measuring a thin plate-shaped object to be measured, a coordinate measuring probe equipped with the coordinate measuring auxiliary tool, and a coordinate measuring machine equipped with the coordinate measuring probe.
2. Description of the Related Art
For example, in a manual operation type three-dimensional coordinate measuring machine, a probe having, at the tip, a ball for contact with an object to be measured being relatively moved manually in a three-dimensional direction, a central coordinate value of the ball being measured at the moment or while the ball being brought into contact or making contact with the object to be measured, and then offset processing is executed for the radius of the ball with respect to the central coordinate value of the ball and a contact position of the ball and the object to be measured can be measured. However, a direction of offset with respect to the measured central coordinate of the ball is required to be pre-specified or to be geometrically calculated with use of measured central coordinate values of a plurality of balls. For example, in the case where the object to be measured is a hole, the ball is guided and brought into contact with three positions of the inside of the hole and each central coordinate value is measured. Next, the center and the radius of a hole circle is obtained by applying the three coordinate values to a circle circulation, and the radius of the hole can be obtained by adding the calculated radius to the radius of the ball.
However, in the case of a thin object, such as sheet metal, having a thickness smaller than the radius of the ball, the probe is required to be guided in the hole measurement so that the tip of the ball is brought into contact with the object to be measured. Therefore, work becomes difficult and skill is required. Additionally, as shown in FIG. 1, with respect to a work 9 which is made of a thin steel plate, if a ball 2 fixed at the tip of a shaft 3 of the probe 1 is brought into contact with the work 9 and measurement is made at a deviated position such as a measurement position 8 and not at a measurement position 7 to which the ball 2 should be made to contact, a problem such as a large measurement error may be caused.
In order to solve the problem, the applicant has proposed, as shown in FIG. 2 or in FIGS. 1 to 3 of Japanese Published Unexamined Patent Application No. H10-62150 (Patent Document 1), that a mark 4 having a predetermined width is attached to the maximum outer circumference of the ball 2 and serves as a standard of measurement.
Additionally, in FIGS. 2 to 5 in Japanese Published Unexamined Patent Application No. 2005-147673 (Patent Document 2), it has been proposed, as shown in FIG. 3, that a ¾ spherical probe formed of the ball 2 which is partially notched to the center C is used, and the center C of the ball 2 is directly made to profile the work 9. In FIG. 3, the reference numeral 11 denotes a push button switch which is provided on a probe body 10 and used for storing current position data only when being pushed.
Further, a V-shaped probe having a V-shaped tip has been put to practical use.
However, in the technology disclosed in patent document 1, an operator is required to visually position the mark 4 of the ball 2 to the work 9 and to entirely concentrate on that, and further, accurate positioning is not easy.
On the other hand, in the ¾ spherical probe disclosed in patent document 2 and the V-shaped probe, it is necessary to work a ball or a tip of a probe into a specific shape, and it is difficult to not only precisely work a center position but maintain the precision.
Further, it is difficult to correct the center position (calibration), and there remains a problem that the total cost increases.